Farmall Electrical System
The Farmall International Harvester uses a 6 volt electrical system with a
Generator and a reverse voltage cutout. The original system had a positive
ground. Yours may or may not have a negative ground depending on the starter
Unlike other systems the switch must be H before the generator will charge.
The switch also has a LO which is low charge but that never worked on my
tractor. Since it does not have a regulator I suspect you were to
switch to low charge when you knew the battery was charged up. You
should be able to see the battery charging by a positive current flow on the
amp meter. The switch has 2 light settings Hi and Dim but Dim just
inserts a resistor in series with the light bulbs and unless you have the
original bulbs you may not notice any change.
DO NOT run the lights without a battery because the system has no voltage
regulator and the voltage from the generator will burn out the 6v light
The generator wire connects to the reverse voltage cutout relay. A wire runs
from the relay to the ON switch and then from the switch to the bat cable to
charge the battery. Wires run from the switch back to the lights. (see diag)
are basically 3 conversions. One involves replacing the generator and the
starter with new 12v types. One only replaces the starter. The other only
changes the battery.
The generator will generate a voltage high enough to charge a 12v battery
(some say it won't but I think it depends on the generator). Since the
system does not have a regulator it only monitors charge current not
voltage. You can install a 12v starter (if you can find one) or use the
existing 6v one as long as don't run it for long times and overheat it,
it turns faster so the tractor starts better. You will need to install
standard 12v light bulbs the sockets are normal bayonet with one point. Same
as parking and backup lights. I found ones that look just like the original
but were 12v at WallMart.
On mine I only changed the battery and the lights and it works fine. But I
use a old battery with a dead cell that would no longer work on my
truck. Or I suggest a 12v Lawn Mower battery since it has lower current.
Most people are converting back to 6v nowadays.
Click on image to view the Farmall wiring diagram. This is my own
modified simplified versions.
Some tractors had a different
generator that ran the lights without a battery and no starter. The same
wiring harness was used and the F wire was not connected. The generator did
not use a relay and had only 1 connection. I suspect that all of those have
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